1. Field of the Invention
The present invention relates to a sewing machine needle free from stitch skipping and fabric yarn breakage.
2. Description of the Related Art
Sewing machines used in sewing are roughly classified into ones for industrial use and ones for domestic use.
The industrial sewing machines are generally used at high-speed rotational speed from the viewpoint of pursuing productivity, and the rotational speed thereof may come up to as high as 8000 rpm. In automated industrial sewing machines, seams are formed in multi-directions but loops that are important for formation of the seams apt to become unstable under the influence of sewing threads having a certain twist angle.
A fabric feeding mechanism of automated sewing machines such as pattern seamers or cycle sewing machines employs an X-Y table to realize multi-directional sewing. When a tip of a rotary hook passes a scarf of a sewing machine needle, minute oscillations of the X-Y table cause a large shaking of the needle from the scarf thereof toward the needle point thereof. As a result, the tip of the rotary hook fails to catch a loop so that stitch skipping is liable to occur.
In order to suppress such stitch skipping arising from the shaking of the needle, the dimensions of a needle dropping hole of the rotary hook are lessened with respect to the thickness of an eye portion at the tip end of the sewing machine needle so that the clearance therebetween is decreased to reduce the shaking of the needle. This means that the thickness of the eye portion at the tip end of the needle is a critical factor for the sewing machine needles.
On the contrary, the household sewing machines have seldom experienced such problems so far unlike the industrial sewing machines since the former is basically used at a low rotational speed. Recently, however, more and more household sewing machines have come to employ an additional embroidery function. Since their mechanisms are similar to those of the automated sewing machines of the industrial sewing machines, the degree of severity for the sewing machines needles is increasing.
A variety of materials used for sewn products have diversely been developed. Recent tendency is toward frequent development of materials rich in stretchability, which have come to be used for sewn products called heavy products such as jeans, which use has not hitherto been present by any means.
Extremely delicate jersey-based materials have also come to be used for automobile seats and have posed another essential problem of fabric yarn breakage in addition to the sewing problems such as stitch skipping and needle breakage. Thus, recent years have not required addressing only a single sewing trouble as before but have required a high-quality sewing machine needle capable of effectively coping especially with combined troubles of stitch skipping and fabric yarn breakage.
In order to solve the stitch skipping problem accompanying speedup and multifunction of the sewing machines as well as diversification of materials, the conventional art has also developed for example a sewing machine needle as shown in FIG. 13A which has a scarf 53 positioned, toward a shank, adjacent to a needle eye 51 formed at the tip end of a blade 50, the scarf 53 being formed on the opposite surface to the surface on which a long groove 52 is formed, and a sewing machine needle as shown in FIG. 13B which has a scarf 53 further deepened by protruding a reverse side of the scarf 53 in the form of a crank 54.
In the case of attempting to deal with further speedup and multifunction of the sewing machines and further material diversification, effective functions and qualities are required to suppress not only the stitch skipping but also the fabric yarn breakage. However, satisfactory measures could not be provided for the combined troubles of stitch skipping and fabric yarn breakage merely by forming the scarf 53 as in FIG. 13A or deepening the scarf 53 by the presence of the crank 54 as in FIG. 13B.
With the sewing machine needle shown in FIG. 13A, puncture resistance is so small due to the absence of the crank that the fabric yarn breakage may seldom occur, but the scarf 53 can not be formed to be very deep, making it impossible to thoroughly eliminate the occurrence of the stitch skipping.
With the sewing machine needle shown in FIG. 13B, the stitch skipping can effectively be suppressed since the deep scarf 53 can be formed by the presence of the crank 54, whereas the puncture resistance becomes larger due to the crank 54 protruding to a great extent and the fabric yarn breakage easily occurs. Furthermore, when the height of protrusion of the crank 54 is increased to obtain a deeper scarf 53, a throat plate and a rotary hook in general use may become unusable, which may possibly require frequent replacement with dedicated parts suited for this type of sewing machine needle, posing a problem in terms of the handling and operability.
For the purpose of solving the combined troubles of stitch skipping and fabric yarn breakage, another type of sewing machine needle has also been proposed which includes a scarf and a crank and which has a curved concave portion formed at an eye web portion of the sewing machine needle to thereby lower the resistance occurring when the needle penetrates the fabric (see, e.g., Japanese Patent Application Laid-Open Publication No. 2000-325685). It is however difficult for this sewing machine needle to completely solve the combined troubles of stitch skipping and fabric yarn breakage.
The above-described deepening of the scarf is generally known as a measure for solving the combined troubles of stitch skipping and fabric yarn breakage caused by the speedup and multifunction of the sewing machines and the diversification of materials. In the case of the sewing machine needle free from the crank as in FIG. 13A, however, if the scarf 53 is deepened, the thickness of a portion of the blade having the scarf 53 formed therein becomes thin, resulting in the strength thereof being lowered, which may possibly bring about frequent needle breakage or frequent stitch skipping due to its insufficient strength.
Even though the scarf 53 is deepened by the formation of the crank 54 as shown in FIG. 13B, the needle may not penetrate a fabric 55 straight since the needle is subjected to an increased resistance at the crank 54 when it passes through the fabric 55, whereby the needle is bent during penetrating the fabric. When the needle is excessively bent, the needle is brought into a direct collision with the throat plated or a needle guard, resulting in a needle breakage.
As set forth above, more all-round functions and qualities are required for the sewing machine needles used in the current sewing machines which operate at enhanced speeds and which are made multifunctional, in combination with the diversified materials.
Requirements of sewing machine needles suited to the high-speed sewing machines are to have an ability to form loops required for the seam formation with desired dimensions and with less deviation, as well as to have a sufficient strength for withstanding high-speed motions.
Requirements of sewing machine needles suited to the multi-directional sewing machines are to have a well-balanced strength in all directions through 360 degrees and to have a deep scarf serving to prevent the stitches from skipping even though any leaning loop occurs since, due to the certain twisted directions of the sewing thread, loops will lean when the amount of the sewing thread used for the loop formation is too much, with the result that the stitch skipping is prone to occur.
Heretofore, plain weave fabrics, moquette, tricot, carpet, leather, etc., have been used as materials for the automobile seats. These materials have rarely experienced the fabric yarn breakage problem even though relatively thick sewing machine needles have penetrated them. With remarkable progress of the materials as described above, jersey-based materials have often come to be used in recent years, resulting in frequent occurrence of the fabric yarn breakage problem in sewing using such materials. Although as a measure against such situation, thinner sewing machine needles of No. 2 to No. 5 count have been used, there still remain secondary problems such as stitch skipping and needle breakage because of the sewing machine needles having insufficient strength.
Similar problems have been seen in the field of jeans sewing or shoes sewing, and the combined troubles of stitch skipping and fabric yarn breakage have been a traditional major problem in knit fabric sewing and foundation garment or lingerie sewing.